1. Field of the Invention
The present invention relates to a proposal of an optical lens having a new structure. In particular, the present invention is directed to the optical lens preferable for using the semiconductor light-emitting elements such as a light emitting diode (LED). Further, the present invention pertains to a light-emitting unit using the lens and lighting equipment using the light-emitting unit. Still further, the present invention relates to an optical information system embracing the light-emitting unit and a light-receiving unit.
2. Background-Art
Flashlights having slender bodies employing halogen lamps are marketed recently. But, these kinds of flashlights have disadvantages such that the life of the batteries are short such as around 3 hours, and the life of halogen lamps are short themselves, in continuous lighting operation conditions.
On the other hand, to personal computers, word processors, small portable televisions, vehicle-mounted televisions, the liquid crystal display (LCD) units are popularly used. For the illumination of a liquid crystal display substrate, a fluorescence discharge tube (a fluorescent lamp) is used as the backlight. There is a problem that the fluorescent lamp for the backlight is easily damaged, or is easily deteriorated in the performance, when the personal computer or the portable television installing the fluorescent lamp is dropped. In addition, when it is operated under low temperature environment of winter season in cold districts, the emission of light efficiency becomes low, because the mercury vapor pressure in a tube becomes low, making it impossible to get enough brightness. Furthermore, stability and reliability are insufficient for a long time operation. In addition, as for the most important problem, the power consumption is large. If a portable personal computer is taken an example, a power consumption of the LCD unit is overwhelmingly larger than electricity used in the microprocessor or in the memory. In view of above situation, it is difficult to operate for long time the portable television or the portable personal computer by a battery when the fluorescent lamp is used as backlight illumination. In addition, a fluorescent lamp operates with pulse like emission of light, corresponding to the frequency of a power supply. Therefore, although there may be differences between individuals, the flickering feeling causes a problem of fatigue of human eyes. That is to say, for the application which is near to direct lighting method such as the backlight illumination, there is a problem of influence to the human body coming from fatigue of the eyes by directly looking the light from the fluorescent lamp for a long time, or coming from the fatigue itself of the eyes.
Since the semiconductor light-emitting element such as the light emitting diode (LED) convert the electric energy directly into light energy, compared with the incandescence lamp such as the halogen lamp, or the fluorescent lamp, the semiconductor light-emitting element has high conversion efficiency and characteristics being not accompanied with generation of heat at the emission of light. In an incandescent lamp, because the electric energy is once converted into the heat energy, and the light radiation due to the generation of heat is used, the conversion efficiency of the incandescent lamp to the light is theoretically low, and the conversion efficiency cannot exceed 1%. Similarly, because the electric energy is converted once into electric discharge energy in the fluorescent lamp, the conversion efficiency of the fluorescent lamp is low. On the other hand, in the LED, it is possible to achieve the conversion efficiency of more than more than 20%, which is about 100 times higher than the incandescent lamp or the fluorescent lamp. Furthermore, because the semiconductor light-emitting element such as the LEDs can be considered that the life is almost semi permanent, and there is no problem of flickering such as the light from the fluorescent lamp, it may be called that the light emitted from the semiconductor light-emitting element is “the light-mild-to-human”, which does not give bad influence to human eyes and body.
Although the LED has such superior features, applications of the LEDs are limited to extremely limited fields, such as the indication lamps on the control panel in various apparatuses or the display unit such as the electric signboard, and there are few examples in which the LEDs are employed by lighting equipments (illumination apparatus). In a part of application, LED products for illuminating keyholes are known recently, but only small areas can light up by the LED products. In this way, apart from the special example, generally the LED is not employed for illumination.
The above situation is ascribable to the fact that, even the brightness of the LED is extremely high, since the light-emitting-area of a single LED is small of around 1 mm2, the enough light flux required for the lighting equipment not being obtained.
In this way, with the conventional optical system, the illumination intensity on an object plane of illumination does not reach desired illumination intensity by the emission of light of a single LED. In other words, a light flux per a unit area on a plane to be lighted up by the light is not enough.
If the lighting equipment, in which a plurality of LEDs are arranged in the matrix form, is provided specific illumination intensity will be obtained. However, as for the main material of the LED, an expensive compound semiconductor is used for the present, and there is a definite limit in reduction of production cost of the LED, because advanced manufacture technologies such as an epitaxial growth and impurities diffusion are required. Furthermore, in a substrate of an epitaxial growth of the gallium nitride, which is materials of a blue LED, an expensive sapphire substrate is used, and there are other situations peculiar to each semiconductor materials.
Therefore, it is not realistic to assemble the lighting system (lighting equipment) by the manner arranging a lot of expensive LEDs in order to get desired illumination intensity, because it becomes too expensive. In addition, although in silicon (Si), a wafer of a diameter of 300 mm begins to be employed, as epitaxial growth substrate of the compound semiconductor, which is required for the material of the LED, such a large diameter wafer cannot be obtained in the present technical situation. Furthermore, there are problems on manufacturing technology such as the homogeneity of epitaxial growth, it is difficult to manufacture the LED having a large luminescence area fundamentally.